Molecular variation of Bothriocephalus acheilognathi Yamaguti, 1934 (Cestoda : Pseudophyllidea) in different fish host species based on ITS rDNA sequences

The molecular variation in Bothriocephalus acheilognathi Yamaguti, 1934 from 11 species of freshwater fish collected in Australia, China, the Czech Republic, England and Hawaii was investigated by determining the nucleotide sequences of the internal transcribed spacer region. The length of the first and second internal transcribed spacer sequences of multiple individuals ranged from 553 to 571 bp and 553 to 615 bp, and the G + C content from 53.1 to 53.5%. The percentage sequence divergence varied between 0 and 0.9% in the ITS1 and 0 and 6.6% in the ITS2, respectively, indicating the occurrence of intraspecific variation. It is demonstrated that the fragment length variation resulted primarily from microsatellite polymorphisms present in the ITS region, especially in the ITS2 region. Phylogenetic analyses revealed that B. acheilognathi examined in this study consisted of three closely related genotypes with certain degrees of host-specificity, and the genotype representing isolates from Cyprinus carpio L. was the most common and diverse form within the species B. acheilognathi.

Molecular systematics of Xenocyprinae (Teleostei : Cyprinidae): Taxonomy, biogeography, and coevolution of a special group restricted in east Asia

We surveyed mitochondrial DNA (mtDNA) sequence variation in the subfamily Xenocyprinae from China and used these data to estimate intraspecific, interspecific, and intergeneric phylogeny and assess biogeographic scenarios underlying the geographic structure of lineages. We sequenced 1140 bp of cytochrome b from 30 individuals of Xenocyprinae and one putative outgroup (Myxocypris asiaticus) and also sequenced 297 bp of ND4L, 1380 bp of ND4, 68 bp of tRNA(His), and 69 bp of tRNA(Ser) from 17 individuals of Xenocyprinae and the outgroup (M. asiaticus). We detected high levels of nucleotide variation among populations, species, and genera. The phylogenetic analysis suggested that Distoechodon hupeinensis might be transferred to the genus Xenocypris, the taxonomic status of the genus Plagiognathops might be preserved, and species of Xenocypris and Plagiognathops form a monophyletic group that is sister to the genus Distoechodon and Pseudobrama. The introgressive hybridization might occur among the populations of X. argentea and X. davidi, causing the two species to not be separated by mtDNA patterns according to their species identification, and the process and direction of hybridization are discussed. The spatial distributions of mtDNA lineages among populations of Xenocypris were compatible with the major geographic region, which indicated that the relationship between Hubei + Hunan and Fujian is closer than that between Hubei + Hunan and Sichuan, From a perspective of parasite investigation, our data suggested that the fauna of Hexamita in Xenocyprinae could be used to infer the phylogeny of their hosts. (C) 2001 Academic Press.

Seasonal variation in kinetic parameters of alkaline phosphatase activity in a shallow Chinese freshwater lake (Donghu Lake)

Seasonal variation of the kinetic parameters of total alkaline phosphatase activity (APA) was studied in a shallow Chinese freshwater lake (Donghu Lake). At the three experimental stations the values of V-max of APA were higher and the negative correlation between orthophosphate and the total APA specific activity (V-max/Chl.) was stronger during summer (from June to September) P depletion. At the same time, the values of Michaelis constant (K-m) of APA at the three stations decreased. Phytoplankton seem to compensate for their phosphorus deficiency not only by an increase in enzyme production but also by an improved ability to use low substrate concentrations. (C) 1997 Elsevier Science Ltd.

FREQUENCY RESPONSE OF FIBER RING RESONATOR AND ITS APPLICATION IN DFB LASER WAVELENGTH VARIATION MEASUREMENT

Frequency response of a fiber ring resonator (FRR) composed of an ordinary optical coupler and a segment of optical fiber is theoretically and experimentally investigated. The frequency response equation based oil small-signal modulation is derived and studied in detail. It is shown that the shape of the frequency response curve is very sensitive to the wavelength; as a result, the FRR can be applied to measure the wavelength of a lightwave source with high resolution. With this method, we demonstrate the measurement of tiny changes of wavelength of a DFB laser. (C) 2009 Wiley Periodicals. Inc. Microwave Opt Technol Lett 51 2444-2448, 2009 Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24608

Effect of the variation of temperature on the structural and optical properties of ZnO thin films prepared on Si (111) substrates using PLD

ZnO thin films were prepared on Si (1 11) substrates at various temperatures from 250 to 700 degrees C using pulsed laser deposition (PLD) technique in order to investigate the structural and optical properties of the films. The structural and morphological properties of the films were investigated by XRD and SEM measurements, respectively. The quality of the films was improved with the increase of the temperature. By XRD patterns the FWHMs of the (0 0 2) peaks of the ZnO films became narrower when the temperatures were above 500 degrees C. The FWHMs of the peaks of (0 0 2) of the films were as narrow as about 0. 19 degrees when films were grown at 650 and 700 degrees C. This indicates the superior crystallinity of the films. The optical properties of the films were studied by photoluminescence spectra using a 325 nm He-Cd laser. The two strongest UV peaks were found at 377.9 nm from ZnO films grown at 650 and 700 degrees C. This result is consistent with that of the XRD investigation. Broad bands in visible region from 450 to 550 nm were also observed. Our works suggest that UV emissions have close relations with not only the crystallinity but also the stoichiometry of the ZnO films. (c) 2005 Elsevier Ltd. All rights reserved.

Electron mobility related to scattering caused by the strain variation of AlGaN barrier layer in strained AlGaN/GaN heterostructures

Using the measured capacitance- voltage curves of Ni Schottky contacts with different areas on strained AlGaN/ GaN heterostructures and the current- voltage characteristics for the AlGaN/ GaN heterostructure field- effect transistors at low drain- source voltage, we found that the two- dimensional electron gas (2DEG) electron mobility increased as the Ni Schottky contact area increased. When the gate bias increased from negative to positive, the 2DEG electron mobility for the samples increased monotonically except for the sample with the largest Ni Schottky contact area. A new scattering mechanism is proposed, which is based on the polarization Coulomb field scattering related to the strain variation of the AlGaN barrier layer. (C) 2007 American Institute of Physics.

Spatial variation of optical and structural properties of ELO GaN directly grown on patterned sapphire by HVPE

A 275 mu m thick GaN layer was directly grown on the SiO2-prepatterned sapphire in a home-built vertical hydride vapour phase epitaxy (HVPE) reactor. The variation of optical and structure characteristics were microscopically identified using spatially resolved cathodeluminescence and micro-Raman spectroscopy in a cross section of the thick film. The D X-0(A) line with the FWHM of 5.1 meV and etch- pit density of 9 x 10(6) cm(-2) illustrated high crystalline quality of the thick GaN epitaxial layer. Optically active regions appeared above the SiO2 masks and disappeared abruptly due to the tapered inversion domains at 210 - 230 mu m thickness. The crystalline quality was improved by increasing the thickness of the GaN/sapphire interface, but the region with a distance of 2 mu m from the top surface revealed relatively low quality due to degenerate surface reconstruction by residual gas reaction. The x-ray rocking curve for the symmetric (0 0 2) and asymmetric (1 0 2) reflections also showed good quality and a small wing tilt of the epitaxial lateral overgrowth (ELO) GaN.

Variation of Optical Quenching of Photoconductivity with Resistivity in Unintentional Doped GaN

The optical quenching of photoconductivity under dual illumination in GaN samples with different resistivity is investigated to reveal the variation of deep levels. The samples are grown by metal organic chemical vapour deposition without intentional doping. Quenching bands centered at 1.35 eV, 1.55 eV, 1.98 eV, and 2.60 eV are observed. It is found that the 1.98 eV quenching band is dominated in all the samples and the 2.60 eV band is observed only in the high-resistivity samples. The possible defect levels responsible for the quenching bands and the origin of different quenching behaviour at 2.60 eV are discussed. It is suggested that the defect level responsible for quenching at 2.60 eV plays an important role for the enhancement of resistivity.